Helical gear compressor or motor



June 28, 1949. G. K. w. BOESTAD 2,474,653

- HELICAL GEAR COMPRESSOR 0R MOTOR Filed April 19, 1946 E'Sheets-Sheet 1 June 28, 1949. G. K. w. BOESTAD 2,474,653 HELICAL GEAR COMPRESSOR 0R MOTOR Filed April 19, 1946 5 Sheets-Sheet 2 June 28 1949. cs. K. w. BOESTAD 2,474,653

HELICAL GEAR COMPRESSOR OR MOTOR Filed April 19, 1946 3 Sheets-Sheet 5 Patented June 28, 1949 UNITED STATES PATENT OFFICE HELICAL GEAR COMPRESSOR OR MOTOR Gustav Karl William Boestad, Lidingii, Sweden, assignor, by mesne assignments, to Jarvis 0. Marble, New York, N. Y., Leslie M. Merrill,

Fig. 3 is a view taken Westfleld, N. 1., and Percy H. Batten, Racine,

Wis., as trustees Application April 19, 1946, Serial No. 663,369 In Sweden April 26, 1945 lates to such devices in which the working spaces are deflnedin part by a casing end wall at the high pressure endof the rotors and which may also be defined in part by sucha wall at the low pressure end of the rotors. An example of such device is disclosed in U. 8. Patent No. 2,174,522, granted to Alf Lysholm.

i It is the generalobiect of the present invention to improve the emciency-of such devices by new and improved porting arrangements opera-* tive to reduce the dynamic losses, as hereinafter explained, and since the principles of the invention are applicable in the same way to produce improved performance whether the device is operated as a fluid compressor or as a fluid actuated motor, it will be suilicientfor the purpose of explaining the invention to describe it as applied to a device operated as a compressor. The manner in which the general and more detailed objects of the invention are secured, together with the advantages to be derivedfrom its use, will appear more fully as the following portion of this specification, which is to be read in conjunction with the accompanying drawings, proceeds.

In the drawings: I a

Fig. 1 is a top plan view of a device embodying .the invention;

Fig. 21s a side elevation of the device shown in Fig. 1; i i i on line 3-3 of Fig.1; Fig. 4 is aview taken on line l'-4 of Fig. 1;

, Fig. 5 is'a view of the top half of the casing,

viewed from below and with the rotors removed; Fig. 6 is a view of the bottom half of the cas-' ing viewed from above and with the rotors removed; and H Fig. 7 is a view showing the rotors. One of the basic characteristics of devices 0 the kind to which this invention relates is that the lntermeshing rotorsthe grooves of which provide the working chambers, are of the type in which one rotor, usually referred to as the male rotor,is provided with lands and grooves 14 Claims. (ciao-143i the major portions of which, and preferably substantially in their entirety, lie outside of the pitch circle. or in other words in the addendum region of the rotor, while on the other hand the cooperating or female rotor has the major portions or substantially all of its lands and grooves 10-- cated within the pitch circle, in the dedendum region of the rotor. v

1 Such rotors,as will hereinafter appear, provide flow characteristics quite difierent from those produced by rotors of the twin or Roots type, and in brief it may be stated that in one aspect of theinvention Iaccomplish the desired objects by providing es for flow of fluid to or from the working chambers through passages located and arranged that the flow is lateral and generally tangential with reference to the addendum region of the male rotor. In another aspect, I obtain improved results by providing the fluid passages communicating with the parts with throats locatedas near as conveniently possible to the ports, such throats providing the minimum cross-sectional area of the passages and having areas so related to the volumetric capacity of the rotor grooves that the velocity of fluid flow through the throats approximates the velocity of travel of the addendum region of the male rotor. From such throats, on the side away from the port with which the throat communicates, the fluid passages are preferably made of nozzle-like or difl'user form, for most emclent conversion of the kinetic energy of the fluid to static pressure energy, or vice-verse, as the case may be. In still another aspect, I employ port contour designed to preserve, as far as possible, uniformity of speed of fluid between the grooves of the male rotor and the throat portions of the communieating passages, thereby reducing or substantially eliminating dynamielosses occasioned bylocal I principles ofthe invention to apractical device I have shown in the accompanying drawings one example, which will be described in its operation as a compressor, but it will be understood that the specific design shown is illustrative only and not limiting as to the scope of the invention, some of the features of whichmay be used to the exclusion of others. and which is defined by the appended claims.

Referring now to the drawings, the compressor comprises a casing indicated generally at and in the embodiment illustrated consisting fa middle section l2, and inlet and outlet end sections l4 and I6 respectively. The middle section is formed'with two parallel cylindrical and intersecting bores the outlines of which are shown by the lines 18 and 20 in Figs. 3 and 4. The inlet and outlet sectionshave plane end walls 22 and 24 forming and closures and cooperating with the side or radial walls in the middle section to form intersecting barrels for the reception of the helically grooved rotors indicated generall at 2 6 and 28 (Fig. 7), 26 being the male rotor and 28 the female. In the example shown the rotors each have four lands and grooves, and the tooth or land profile shown is that disclosed in the" aforesaid Lysholm patent. The invention is, howevenindependent of specific tooth profile and the number of grooves per rotor, which may be the same or different in two intermeshing rotors.

Rotors 26 and 28 are mounted for rotation in the respective barrels by means of suitable bearcycle of operation is divided into four phases,

(1) the inlet or induction phase during which the rotor grooves are filled through the inlet port as the grooves pass the port, (2) the transport phase during which the fluid is carried at constant volume peripherally after the grooves have passed out of communication with the inlet port and before they communicate with the outlet port, (3) the compression phase, during which discharge passage through the outlet port as the chambers are reduced to final vzero volume by the action of the intermeshing grooves and lands. It is with the first and last of the-above described phases that this invention is particuings in the end sections of the casing, in known manner, and are maintained in properly spaced rotational relation by the usual timing gears located in the housing section l6. Such construction is conventional and need not be illustrated in detail for an understanding of this invention As willbe seen particularly from Figs. 1 to 3, the casing structure provides a laterally extending inlet or inductionpassage 30 having walls converging in the direction of gas flow to give smooth contraction of cross-sectional area to the throat 32. In the embodiment illustrated this passage is formed partly in the end section and partly in the middle section of the casing, and communicates with an inlet port having portions located in the side and one end wall of the barrels housing the rotors. The configuration of the end wall portion'of the port is shown by, the line of the portion of the port in the side wall is shown by the line k--l-m-1t-o in Fig. 5,.the-port thus providing both radial and axial communication with the working chambers formed by the rotor grooves.

At the outlet or discharge end the construction is generally similar to that just described, providing, an outlet passage 34 of smoothly increasing or diffusorlike section leading from the throat 36 which communicates with a combined larly concerned in one of its aspects, and for purposes of explanation, the application of certain principles of the invention to the discharge phase of the operation will first be considered. In the operation of the device as a compressor, the rotors turn in the directions indicated by arrows 38 and 40 in Fig. 4 and the trapped volumes of fluid, being compressed in the grooves 42 of the male rotor and grooves 44 of the female rotor, are traveling at the respective peripheral velocities of the different grooves. In this connection it is highly important to note that because of the fundamental characteristic of this type of device,

1. e., that the grooves of the male rotor are in the addendum region and the grooves in the female rotor are in the dedendurn region, the peripheral speed of the male grooves is always very considerably greater than that of the female grooves. This holds true regardless of the relative number of grooves and the relative diameters of the two rotors. In any design such as that illustrated, wherein the two rotors have the same number of grooves, their rotative speeds will be the same and the female rotor will be of smaller diameter than the male. With other combinations of groove numbers in the respective rotors the female mayv have more grooves than the male and may be of larger diameter, but in such case the female rotor will turn at a lower number of revolutions than the male; so that in all cases where male and female rotors are employed the peripheral speed of the female grooves will be less than that ,of the male grooves, since one set is traveling within the pitch circle and the other set is traveling outside the pitch circle. Also itis to be noted that the volumes of the male grooves are in most cases substantially greater than the volumes of the female grooves. Devices of the kind under consideration operate at relatively high speeds, peripheral speeds for the tips or crests of the male rotor lands in the substantially all communication through an end wall port or through a side wall port. Insofar as the nature of the passage leading to the port is, concerned, the present invention applies equally to radial, axial and combined forms of ports, different types of which may be used for the inlet and outlet of the same device.

The general principle of operation of the: described device is well known and need not be given here in detail, but it may be said that the range'of from to 200 meters per second or even higher being desirable, maximum speed in many cases being limited only by Practical considerations such as the life of high speed bear ings and the like. Since the kinetic energy represented by the inertia of a moving body varies as the square of its velocity, it will readily be seen that in a device of the kind described the kinetic energy of the masses of gas in the male grooves is much greaterthan that in the female grooves since ordinarily the masses are greater and in all cases the peripheral speed is materi-' calculation to so relate the area of the throat to the volume delivered. from or inducted to the grooves that the desired relation between the peripheral velocity of the male grooves and the velocity of flow through the throat is obtained.

While the arrangements-and dimensions of passages to and from the working chambers just 8 first come into communication with an outlet port. From Fig. 7 it will-be seen that with the port configuration provided, the male rotor grooves are covered by the side well over the area lc--l--:c, which would be open port area if the previously used triangular form of port were employed, while the female grooves are covered by the wall area mn'--o'-y, which described contribute substantially to improved performance, the port configuration-is also important in reducing dynamic losses between the working chambers and the throats of the passages. This .is particularly true with reference to side wall or radial port configuration. In previous constructions, the edges of the radial port have been made angular throughout their length, in substantial conformity with the angularity of the lands of the rotors, so that the grooves of the rotors, would come into registry with the port substantially simultaneously along the entire length of both sides of the port. Such porting configuration is illustrated in the Lysholm Patent No. 2,174,522 previously mentioned and also in Lysholm Patent No. 2,243,874. These arrangements have been proposed, however, primarily with the thought in mind of securing quick opening of the port and elimination of loss through Wire drawing. I have found, however, that improvement in performance is obtained if a narrower and more elongated form of port is employed, which operates to maintain more uniform velocity of flow from the rotor grooves to the throat of the outlet passage (or vice versa) than the generally triangular form of port heretofore employed. In order to illustrate what I believe to be the reason for this I have shown in Fig. "I, the discharge ends of two cooperating rotors 26 and 18 with the outline of the radial outlet port shown thereon by the dotted line lc'--l'm-n'-o'.- The direction of rotation of the rotors is shown by arrows 38 and 40. As the rotors revolve, the crest or apex 50 of one male rotor land passes underneath the leading edge 5! of the crest of a cooperating female land to enter the female grooves 56, which is already in communication with the port, as is also the male groove 58 ahead of the crest 50. The point of intersection of these two edges advances axiallytoward the discharge end wall 24 as the rotors revolve and the fluid dis placed from between the approaching faces of the lands tends to flow axially as indicated by arrow 60. The same character of flow is produced by the intersection of the next succeeding. intersecting edges 50a and 54a as indicated by arrow 60a. At the outlet end of the rotor grooves, however, the direction of movement of the fluid is at right angles to the rotor axes, as indicated by arrows 62 and 64, this direction of flow being imposed by the end wall 24 until communication with an axial end wall port is established. As a result, the directions of the average flow may approximate those of arrows 66 and 68, and for this average flow it is desirable to maintain as nearly as possible a uniform velocity of travel to and through the port'to .the outlet throat. To this end the present port outline contributes by covering the portions of the grooves adjacent to the outlet end of the rotors, after they have would otherwise be open port area. The portion of the port edge l'm' is preferably diagonal as shown, on a lint approximating the helix angle of the male rotor lands, so that initial opening of the port to a substantial area will be effected by a comparatively few degrees of rotor movement.

The position of the sealing line between intermeshing pairs of lands and grooves is indicated by line Z and as will be seen from Fig. 7, this creates a pocket extending axially behind the point of intersection of the crests of the lands. This pocket advances toward the discharge end as the rotors revolve and finally runs out to zero volume. In order to facilitate discharge from this pocket, the port edge is advantageously made diagonal along the line :n'o.

While in the example shown the side edges of the port are parallel with the'rotor axes, the speciflc outline may be changed without departing from this phase of the invention, the principal criterion being that the port outline be such as to maintain a velocity of flow through the port approximating that of the fluid in the grooves delivering to it. Generally speakin this is accomplished by shaping the side wall port so that the grooves first open into the port at a place axially spaced from the ends of the rotors and thereafter progressively register withthe port in the direction toward the rotor ends.

In the compressor illustrated, the peripheral extent of the end wall portions of the ports and the axial length of the side wall portions of the ports are so related to the helix angle of the grooves that both portions of each port register simultaneously with any given groove. This however is not essential and depending upon specific factors of design such as the compression ratio desired, speed of operation, the number of lands and grooves in the different rotors, helix angles, etc., this relation of the time of opening or closing of the different parts of a combined radial-axial port may readily be changed by altering the relation between the length of the radial part and th peripheral extent of the axial part.

While as has previously been noted, the device has been described in its action as a compressor, it will readily be apparent that the same principles apply to its action as a motor, in which case the rotors are revolved in directions opposite those shown herein and the port at the high pressure end becomes the inlet rather than the outlet port, while the low pressure port becomes the outlet port. In such case the same flow factors apply in reducing dynamic losses bothwith respect to the admission of high pressure motive fluid to the working chambers and the exhausting of the exthe side of said casing structure providing said second barrel and away from the plane common to the axes of said rotors. a

2. In a rotary device, acasing structure providing two parallel intersecting barrels and having inlet and outlet ports communicating with i said barrels, a male rotor having helical lands and grooves the major portions of which lie outside the pitch circle of the rotor and mounted for rotation in a Mom of said barrels, a female rotor having helical lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one of said barrels and intermeshing with said male rotor, a fluid conducting e in said casing structure communicating with omelet said ports and extending therefrom in a laterally inclined direction toward the side of said casing structure providing said second barrel and away from the plane common to the axes of 1 said rotors, said passage also being inclined longitudinally of the rotors in adirection away from the longitudinally central portions thereof.

3. In a rotary device, a casingstructure providing two parallel intersecting barrels, a male rotor having helical lands and grooves the major portions of which lie outside the pitch circle of the rotor and mounted for rotation in a first one of said barrels, a female rotor having helical' lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one ofsaid barrels and intermeshing with said male rotor, inlet and outlet ports in said casing structure communicating respectively with t, the opposite end portions of said barrels on re- ,rel and in oppositely inclined directions away from said plane.

'4. In a rotary device, a casing structure providing two parallel intersecting barrels, a male rotor having helical lands and grooves the major portions of which lie outside the pitch circle of the rotor and mounted for rotation in a first one of said barrels, a female rotor having helical lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one of said barrels and intermeshing with said male rotor. inlet. and outletports in said casing structure communicating respectively with the opposite end portions of said barrels on respectively different sides of the plane common to the rotor axes, and fluid conducting passages communicating respectively with said ports and extending therefrom laterally toward the side of said casing structure providing said second barrel and in oppositely inclined directions away from said plane, at least oneof said passages also being inclined longitudinally of the rotorsin a direction away from the longitudinally central portions thereof. a

5. In a rotary device, a casing structure pro- 10 portions of which lie outside the pitch circle of the rotor and mounted for rotation in a first one of said barrels, a female rotor having helical lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one of said barrels and intermeshing with said male rotor, inlet and outlet ports in said casing structure communicating respectively with the opposite end portions of said barrels 'on respectively difierent sides of theplane common to the rotor axes, and fluid conducting passages communicating respectively with said ports and extending therefrom laterally toward the side of said casing structure providing said second barrel and in oppositely inclined directions away from said plane, said passages also being oppositely inclined longitudinally with respect to each other and away from the longitudinally central portions of said rotors.

6. In a rotary device, a casing structure providing two parallel intersecting barrels and having inlet and outlet ports communicating with said' barrels, a male rotor having helicallands and grooves the major portions of which lie outside the pitch circle of the rotor and mounted for rotation in a first one of said barrels, a female rotor having helical lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one of said barrels and intermeshing with said male rotor,

and a fluid conducting passage in said casing structure communicatingwith one of said ports, said passage having a throat adjacent to the port with which it communicates and a portion of expanding cross sectional area leading from said throat, the portion of said passage between said port and said throat extending laterally in tangential direction from the addendum region of the male rotor toward the side of the casing structure providing said second barrel.

7. In a rotary device, a casing structure providing two parallel intersecting barrels and having inlet and outlet ports communicating with said passage having a throat adjacent to the port with which it communicates providing the minimum cross sectional area of the passage and the area of said throat being related to the displacement of the grooves in said rotors to provide a velocity of fluid flow through said throatapproximating the average peripheral velocity of the grooves in the male rotor.

8. A device as set forth in claim 7 in which said passage is formed toprovide a. nozzle like portion for rotation in a first one of said barrels, a female rotor having helical lands and grooves the major portions of which lie within the pitch circle of the rotor and mounted in a second one 11 of said barrels and intermeshing with said male rotor, and a fluid conducting passage in said casing structure communicating with one of said ports, the port with which said passage communicates providing an opening in the radial walls of said barrels extending longitudinally from one end thereof and of greater length than width and said passage communicating laterally with mimosa said opening from the side of the casing structure providing said second barrel.

10. A device as set forth in claim 9v in which the side edges of the port extend in generally longitudinal direction.

11. A device as set forth inclaim 9 in which the side edges of the port extend in generally longitudinal direction and are connected by an end edge at least the major portion of which extends diagonally at approximately the same angle as the helix angle of the lands of the male rotor.

12. In a rotary'device, a casing structure in cluding side walls and an end wall defining two parallel intersecting barrels and having inlet and in a second of said barrels, said rotors having intermeshing helical lands and grooves cooperating with each other and with the casing side and end walls to form working chambers for fluid varying in volume as the rotors turn, at least one of said ports in said casing structure having portions in both said side and end walls, and a outlet ports communicating with said barrels, a imale rotor in a first of said barrels, a female rotor fluid conducting passage communicating with one a of said ports and leading therefrom in a direction providing a more-direct line of flow of fluid between the grooves of the'inale rotor and said passage than between the grooves of the female rotor and the passage.

13. A device as set forth in claim 12in whichthe direction of said passage is diagonal with respect to the plane common to the axes of said rotors.

14. A device as set forth in claim 12 in which the direction of said passage is diagonal with respect to both the plane common to the axes of said rotors and aplane normal to said axes.

GUSTAV KARL WILLIAM BOESTAD.

Ramayana crrnn I The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 395,956 Day Jan. 8, 1889 1,991,541 Cannizzaro Feb. 19, 1935 2,243,874 Lysholm 1. June 3, 1941 2,410,172 Lysholm Oct. 29, 1946 FOREIGN PATENTS Number Country Date 437,042 Great Britain Oct. 23, 1935 464,476 Great Britain Apr. 16, 1937 464,494

Great Britain Apr. 16, 1937 

